WASHINGTON (AP) — Listeria bacteria was found in Blue Bell ice cream's Oklahoma plant as far back as March 2013. That's according to test results released Thursday by the government.

The company continued to ship ice cream produced in that plant after what the FDA said was inadequate cleaning.

Three deaths are now linked to the ice cream, and the company recalled all of its products last month.

The Food and Drug Administration released results of investigations into Blue Bell's plants in Oklahoma, Texas and Alabama. The most extensive violations were found in Oklahoma, where the FDA listed 16 separate positive tests for listeria on equipment and in ice cream from March 2013 through January 2015.